1. Field of the Invention
The present invention relates to a progressive-power lens to which optical performance specifying information specifying optical performance values such as progressive zone length and an inner shift amount for near vision is attached.
2. Description of the Related Art
Conventionally, an alignment reference mark which is a reference for positioning when the lens is set into a frame, and mark, with which progressive zone length, an inner shift amount for near vision, addition diopter and the like of the lens are identified, are inscribed on the progressive-power lens. Further, more detailed design information is inscribed on lens surfaces (refer to Patent Document 1 and the like).
These marks are inscribed at such positions as they remain within the frame even after the lens is set into the frame. Accordingly, even when the lens is set into the frame and used by a consumer, the consumer can identify the progressive zone length, the inner shift amount for near vision and the like by reading the marks (refer to Patent Document 2 and the like).
As for a method to inscribe the marks as described above on lenses, there are a method of marking with a diamond pen, a method of making an inscription by emitting laser light, and the like (refer to Patent Document 3 and the like).
[Patent Document 1]
Japanese Patent Laid-open No. 11-337887 (pages 1 to 3, FIG. 1)
[Patent Document 2]
Japanese Patent Laid-open No. 2000-284234 (pages 1 to 5, FIG. 1)
[Patent Document 3]
Japanese Patent Laid-open No. 2000-28891 (pages 1 to 7, FIG. 2)
Incidentally, the aforementioned progressive zone length, inner shift amount for near vision and addition diopter are considered to be especially important items in the evaluation of progressive-power lenses.
First, the progressive zone length means the length of the progressive zone which is an intermediate portion between a distance portion and a near portion of the progressive-power lens, and in which the refractive power successively changes. Accordingly, the progressive zone length is an important optical performance value to evaluate how much is it necessary to turn a sight line downward on the occasion of near vision, or how much is it necessary to turn a sight line upward on the occasion of distance vision, when the progress-power lens is used.
The inner shift amount for near vision means the amount by which a near center is slightly shifted to a nose side with respect to a distance center with a convergence amount of an eye being included. This also becomes a large factor to determine the optical performance of the progressive-power lens as the above-described progressive zone length. The convergence means an action of an eyeball to draw near to a nose side when a man looks at a thing near him or her.
The addition diopter means a difference between far vision refractive power and near vision refractive power of the progressive-power lens. The addition diopter is made one item of the prescription values and is an important optical performance value which significantly influences the performance of near vision of the progressive-power lens such as the width of the near range and bow close an object can be seen. Further, considering that as this addition diopter becomes larger, “jitter” and “distortion” at a side portion of a near portion which are disadvantages of the progressive-power lens tend to increase, it is necessary to make the addition diopter a proper value without excess and deficiency. From this point of view, the addition diopter can be also said to be an important optical performance value to the progress-power lens.
As described above, the progressive-power lens has the important optical performance values which are the progressive zone length, the inner shift amount for near vision, and the addition diopter. However, though the marks with which these optical performance values are identified are inscribed on the conventional progressive power lens, the lens cannot be sometimes suitably evaluated based on them by simply looking at the mark. This is because the methods of defining these optical performance values are not always unified and there exist a plurality of defining methods.
Explaining in concrete, concerning the progressive zone length, for example, the conventional progressive-power lens has the following problems.
First, in such a type of progressive-power lens as has a progressive surface only on one of a convex surface or a concave surface, it is normal to define the progressive zone length with a surface having the progressive surface as a reference. However, when the lens is designed and manufactured after receiving an order, even lens having the progressive surface on the convex surface can be designed and manufactured by defining the progressive zone length with the concave surface as a reference. Similarly, even such a type of lens as has the progressive surface on the concave surface can be designed and manufactured by defining the progressive zone length with the convex surface as a reference.
In such a type of lens as creating the progressive refractive performance on both surfaces by combining the refractive performances on the convex surface and the concave surface, it is not that only any one of the surfaces is the progressive surface, and therefore the progressive zone length can be defined with any surface of the convex surface and the concave surface as the reference.
In this manner, the progressive zone length is defined with the convex surface as the reference in some cases, and it is defined with the concave surface as the reference in other cases. It is not always unified which surface is made the reference. However, in the case with the convex surface of the lens being made the reference, and in the case with the concave surface being made the reference, an angle of the sight line passing through a near eye point, which is the amount of how much it is necessary to turn the sight line downward on the occasion of near vision, differs, even when the values of the progressive zone length identified by the marks inscribed on the lens are the same. This problem is the problem similarly occurs to the inner shift amount for near vision.
In concrete, as shown in FIG. 6, a model which directs a sight line to a progressive-power lens 3 from a center of rotation 2 of the eye 1 is assumed. In this model, when a progressive zone length 4 is defined with a convex surface 3a as a reference, the sight lines passing through a distance eye point and a near eye point on the convex surface 3a are what are shown by the reference numerals 5 and 6, respectively. On the other hand, the progressive zone length 4 is defined with a concave surface 3b as the reference, and the sight lines passing through the distance eye point and the near eye point on the concave surface 3b are what are shown by the reference numerals 7 and 8, respectively.
Then, even the definition value of the progressive zone length 4 is the same as shown in FIG. 6, the case in which the progressive zone length is defined with the convex surface 3a as the reference and the case in which the progressive zone length is defined with the concave surface 3b as the reference are obviously different especially from the viewpoint of the angles of the sight lines 6 and 8 for the near vision. Accordingly, there is the problem that the optical performance of the progressive-power lens cannot be accurately evaluated from the concrete viewpoint of how much the sight line needs to be turned downward, for example, on the occasion of the near vision, by only specifying the definition value of the progressive zone length.
Next, concerning the addition diopter, the conventional progressive-power lens has the following problem.
In the markets of Japan and the United States, the addition diopter is normally defined as the difference between the refractive power measured by applying the opening of a lens meter to the reference point of the near portion on the convex surface and the refractive power measured by applying the opening of the lens meter to the reference point of the distance portion on the convex surface, in the progressive-power lenses of the type having the progressive surfaces on the convex surfaces.
However, in Europe, the addition diopter is sometimes defined as the difference between the refractive power measured by applying the opening of a lens meter to the reference point of the near portion on the concave surface and the refractive power measured by applying the opening of the lens meter to the reference point of the distance portion on the concave surface, also for the progressive-power lenses of the type having the progressive surfaces on the convex surfaces.
On the other hand, in the progressive-power lenses of the type having the progressive surfaces on the concave surfaces, the addition diopter is normally defined as the difference between the refractive power measured by applying the opening of a lens meter to the reference point of the near portion on the concave surface and the refractive power measured by applying the opening of the lens meter to the reference point of the distance portion on the concave surface.
In the progressive-power lenses of the type having the progressive surfaces on the concave surfaces, there is the one which is corrected in consideration of a worn state at the time of design. In this case, the difference between the refractive power measured by applying a lens meter to the reference point of the near portion on the concave surface and the refractive power measured by applying the lens meter to the reference point of the distance portion on the concave surface differs from the ordered addition diopter by the amount of correction in consideration of the worn state.
In a lens of the type which make the progressive refraction performance on both surfaces by combining the refraction performances of the convex surface and the concave surface, it is not that only any one surface is the progressive surface, and therefore the addition diopter can be defined with any surface of the convex surface and the concave surface.
Further, there is the method of determining the addition diopter by selecting the optical value of the spectacle lens so that a light wave surface coming into the eyes of a testee at the time of optometry, and a light wave surface coming into the eyes of the testee when the testee wearing the spectacle lens sees an object correspond to each other or an closely analogous to each other, based on the information by what optometry method the addition diopter is determined.
As described above, there are various definition methods of the addition diopter. Accordingly, by only specifying the value of the addition refractive power, it is not always clear by which method the value is defined, and therefore there is the problem that the evaluation reference for the lens differs.